Oscillators are well known devices for providing a reference frequency source. The oscillator typically has a quartz crystal or other resonator and also has electronic compensation circuitry to stabilize the output frequency.
Various methods are known for stabilizing the output frequency as the temperature of the oscillator changes. Temperature compensated crystal oscillators (TCXO) typically employ thermistors which generate a correction voltage that reduces the frequency variation over temperature. The correction voltage is usually applied to a varactor diode in the crystal circuit such that the crystal frequency may be varied by a small amount.
To obtain a more stable output, ovenized oscillators (OCXO) heat the temperature sensitive portions of the oscillator which are isolated from the ambient to a uniform temperature. Ovenized oscillators contain a heater, a temperature sensor, and circuitry to control the heater. The temperature control circuitry holds the crystal and critical circuitry at a precise, constant temperature. The best controllers are proportional, providing a steady heating current which changes with the ambient temperature to hold the oven at a precise set-point, usually about 10 degrees Centigrade above the highest expected ambient temperature.
Despite the benefits of the oscillators available today, there continues to be a need for high performance, reduced size, low cost ovenized crystal oscillators.